Parker Ackley: Bolt Thrust in Rifles

[.56/50 Iron]

Good afternoon!
     Looking through the archives at random for this group, I find there is a lot of concern for the strength of "brass" framed receivers. The question is asked, as I did the other day, what would the proof test chamber pressure be for the .45 Colt in the Uberti Henry. Sensibly, some allowed that the SAAMI pressure limit for the .45 Colt round is the answer. I have not found any discussion of Bolt Thrust here and this measurement may make a lot more sense in regards to how much a brass framed rifle gets stressed as it discharges a round.
     Parker Ackley was a well known gunsmith located in Salt Lake City in the late 50's and into the 60's. He wrote several books, one of which was "Volume One: Handbook for Shooters & Reloaders". His specialty was the development of wildcat rifle calibers which he created and tested and built rifles for. He was also a contributing gunsmithing editor for "Guns and Ammo Magazine" for a number of years. In the handbook I mentioned above in a chapter entitled "Pressure" (page 138 and following), he talks about an experiment he did with an old Model 94 Winchester. Briefly, he removed the locking lugs from the action. Then he rechambered the barrel for his 30-30 Improved (less taper to casing walls than a standard 30-30). With the lugs removed from the action, he fired two standard factory .30-30 cartridges. Prior to shooting, he made sure that the chamber was clean and dry. The rounds he fired formed to the Improved chamber perfectly with no primer back out. Then he unscrewed the barrel one turn and fired two more rounds. The primers backed out equal to one barrel thread, but the cases did not back up against the bolt, which means that the brass case withstood the pressure. Two more factory cartridges were lightly oiled. The primers did not back out, but the shoulders of both rounds were blown forward the distance of one barrel thread. Thus the oiled cases did not adhere to the chamber walls but backed up against the bolt face. Last, he unscrewed the barrel two full turns and cleaned and dried the chamber. He fired two more factory rounds. The 1st casing remained tight in the chamber but the primer fell out. (He lengthened the firing pin to fire the rifle). He then oiled the case of the second round and fired it. The casing stretched and separated just above the base, indicating that it again did not grip the chamber walls and expanded back to the bolt face until it separated. He felt that this experiment proved that a clean, dry chamber will allow a cartridge case to grip the walls of the chamber and not move back against the bolt face in most cases, making the actual back-thrust pressure on the bolt face itself little or none. I think it is the back thrust of the casing on the bolt face, then to the toggle lock-up, that is the pressure we should be concerned about. The actual chamber pressure means nothing (if it is a safe load to begin with) as the barrel and receiver ring area contains all of that pressure itself.
    I'm thinking that the brass framed Henry rifles that we are involved with will have little stress to the lock up area of the action itself if we keep the chamber clean and dry and the ammo that we fire in the same condition. Hot loaded .45 Colt ammo will tend to defeat the design strength of the action and destruction may come with blown chambers/receiver rings. I would bet that in cases like this, the actual movement of the casing back to the bolt face would be minimal until escaping gas from the split casing took over.
    Have you guys read anything that could be added to this?
Regards,
.56/50 Iron

[Pettifogger]

I think you are WAY over thinking this.  The CIP standard (Commission internationale permanente pour l'épreuve des armes à feu portatives 'Permanent International Commission for Firearms Testing') for the .45 Colt is actually higher than SAAMI.  (16,000 psi.)  Millions of rounds of .45 have been fired out of these guns and other than OBDs I have never heard of one actually blowing up.  Contrary to some people's belief the frames do not stretch.  If you look at the bolt it is sticking out in the air for over one and one-half inches totally unsupported.  The links are held together with pins.  Theoretically, the links are supposed to be fitted such that the radius milled in one section of link is bearing on the matching radius on the next piece of link (and in the bolt head and receiver recesses).  As a practical matter virtually all the pressure is on the link pins.  When heavy loads are fired these link pins bend a little and you get slop in the linkage.  The frame didn't stretch, the links compressed.  Don't worry about it, shoot the thing.  You will never have a problem if you are loading to SAAMI pressures.

[.56/50 Iron]

Thank you! So far, everything I have read tells me to relax... Lots of inquiries over time and pretty much the same conclusions.
.56/50 Iron

[pistol1911]

Why not reload with a full case of black powder and quit worrying.

[rbertalotto]

Bolt Thrust has always been the issue.

If you look at the Thompson Contender and the Encore, the Contender could handle just as much pressure, but not as much bolt thrust. Therefore the Contender was limited to case heads of the 223 size or rimmed cases of the 30-30 size and the pressures associated with these cartridges. Along with the 45-70.

But although the chamber pressures of some 308 headsize calibers were the same as 223 head size cases, the larger head size exhibited too much bolt thrust and therefore could not be used in the Contender.

The Encore was a "beefedup" Contender and was able to handle the bolt thrust of 30-06, 308, 270, etc cartridges

Now how about the prohibition of cartridge conversions on brass framed revolvers. I bet the back thrust of a cartridge conversion along with the recoil plate might even be less at CAS levels that shooting these pistols with BP? 

[.56/50 Iron]

Good Evening!
     I guess if you keep your chamber clean and oil free, from what I have read, bolt thrust is not a real problem as the brass clings to the chamber walls and the cartridge case head does not hit the breech bolt face with much pressure, if any at all (as Ackley proved with the firing of standard factory ammo in a Model 94 Winchester .30-30 with no locking "bolts" on each side of the rear of the receiver). If your chamber is oily or filthy, the brass cannot grip the chamber walls, thus is free to move back against the bolt face. I'm going with the theory of the clean chamber and thus very low back thrust against the bolt face.
.56/50 Iron

[Pettifogger]

Gee, hate to burst your bubble but with most cowboy .45 ammo the fired case comes out of the gun covered in soot.  Why, because it is loaded so light the brass doesn't expand and seal the chamber.  Quit fretting over this and shoot the dang thing.  MILLIONS and MILLIONS of rounds have been fired out of the Uberti 60s and 66s.  The receivers ain't gonna stretch and you will be OK.

[MJN77]

 I have owned a couple of brass frame Uberti henry rifles and an 1866 or two ( I currently own a 1866 44-40) over the last twenty years and have never had a problem with any of them. I do not "cowboy" shoot with my guns. I hunt with them. I used factory Remington and Winchester 200 gr. soft point smokeless hunting ammo (average velocity 1180 fps) in them for years. Still, no problem. For the last couple of years I have taken to loading and using nothing but full BP loads with, again, no problems. All modern made guns are made to handle SAAMI spec ammo. If you plan to reload, there is plenty of info about what pressures to load to. Or you could load full BP ammo and not worry about it. The Uberti Henry will shoot any off the shelf .45 colt ammo just fine as long as you don't shoot hot stuff like anything marked as "Ruger only" or Buffalo Bore ammo. If you are really this worried about shooting a brass frame gun, you should probably consider selling it and getting something that you would be more comfortable with. An 1873 or 1892 winchester perhaps?

[.56/50 Iron]

Thanks for the note. I don't shoot cowboy either, but I want to be sure as I follow the reloading manuals for this class of rifle, that I don't overdo it. Your note is quite realistic and you can be sure the Henry will be shot---a lot! I feed a quantity of whitetailed deer year around and provide them with water also. The sights on the Henry (unloaded, of course...) line up quite nicely on them... I have never shot a deer within 10 miles of my home. (Just in case this might cause some to wonder) Not ethical in my way of thinking. I do use blackpowder in some of my rifles, particularly the Sharps .45's and .50's . I tried black in my Spencer, but I got the best, consistent accuracy out of smokeless.
.56/50 Iron

[MJN77]

Thanks for the note. I don't shoot cowboy either, but I want to be sure as I follow the reloading manuals for this class of rifle, that I don't overdo it. Your note is quite realistic and you can be sure the Henry will be shot---a lot! I feed a quantity of whitetailed deer year around and provide them with water also. The sights on the Henry (unloaded, of course...) line up quite nicely on them... I have never shot a deer within 10 miles of my home. (Just in case this might cause some to wonder) Not ethical in my way of thinking. I do use blackpowder in some of my rifles, particularly the Sharps .45's and .50's . I tried black in my Spencer, but I got the best, consistent accuracy out of smokeless.
.56/50 Iron

The 1860 is a great rifle and will more than do the job on a deer as long as you do your part. I have owned three of them (a steel frame and two brass frames) all in 44-40 and all shot very accurately. Only reason I don't own any now is because I like the 1866 a bit better. Like I said, as long as you do not exceed SAAMI pressures, your rifle will outlast you. I personally prefer BP in my rifles because in a 44-40 it will send a 200 grain bullet down range at about 1300 fps and that doesn't turn out very well for the deer. Or groundhog. 

[mtmarfield]

  Greetings!

   Two things that I do before I shoot: I carefully wipe out any excessive oil/lube from the chamber; I also remove sizing oil/lube from the reloaded cartridge before I put the finished round into its box.
   I also shoot a S & W 53 revolver, chambered for the .22 Rem. Jet, and I do the same to the chambers of the cylinder. Result? None of the cylinder binding/lock-up that all of the gun writers complained about.
   It works! Try it.

           Be Well!

                       M.T.Marfield

[Coffinmaker]

Sorry for jumping in "late."  ALL this concern with "bolt thrust" as applied in a theoretical manner to the guns we shoot in the CAS game just doesn't apply.  Whether we are talking Black Powder or Smokeless, the result is the same after firing the first round.  The chamber is fouled.  In the case of light loaded smokeless ammunition, we're talking about really really fouled chambers.  In come cases, it's remarkable the rifle functions the full match.  Usually 60 rounds minimum.  Not two carefully prepared rounds in a meticulously prepared chamber.  Just doesn't translate from a fairly high pressure round to a straight walled pistol round with barely enough pressure to get the bullet all the way thru the bore.
Brass frames. 
Chamber pressures in factory loaded ammo nor correctly loaded reloads simply are not high enough to damage a brass frame.  I personally shoot .45 conversion cylinders in brass frame Cap & Ball guns, but at reduced pressure, in a shorter case with light bullets.  The frames are not going to stretch.  Damage might result with .45 Colt loaded heavy.  Don't do that.
Don't load .45 Colt for an 1866 or an 1860 Henry with a heavy charge of powder and 300Gr hunting bullets.  Stick to factory loaded ammunition or hand loads loaded to factory levers and either an 1866 or a Henry will outlast the shooter.

Coffinmaker